Thermally expandable actuator means for thermal switch



G. AsAKAwA April 28, 1964 THERMALLY -EIXPMIDAlBLE ACTUATOR MEANS FOR THERMAL SWITCH Filed Nov. 2. 1959 INVENTDR. GEORGE ASAKAWA l BY wlLsoN, Laws a RAE ATTORNEYS 3,131,269 t THERMALLY EXPANDABLE ACTUATOR MEAN FOR THERMAL SWITCH George Asakawa, Yellow Springs, Ohio, assignor, by mesne assignments, to Antioch College, Yellow Springs, Ohio, a corporation of Ohio Y Filed Nov. 2, 1959, Ser. No. 850,431

11 Claims. (Cl. 200-113) `This invention relates to mechanisms for converting electrical energy into mechanical movement, and particularly to such mechanisms which utilize electrically-energir/ed therrnallyexpansible cartridges to develop the mechanical movement.

The-re have been devised various devices for converting electrical energy into mechanical movement through the use of dispersed electrically-conductive particles distri-buted throughout a thermally-expansible pellet of wax or other material undergoing substantial expansion in respouse to heat-input. Such devices incorporate spaced tributed ythroughout `the expansible material so that an even, high-ly etteotive heating action is obtained.

The above described devices are sometimes employed in atmospheres of temperature-changing characteristics,

and in many cases it is not desired tha-t the temperature change in the. atmosphere have any effect on the motion produced by the device, i.e. it is desired that the device operate only in response to an electrical energy input and not in response to chan-ge in temperature of the atmosphere. With the devices heretofore developed this characteristic has not always been obtained.

Accordingly it is an object of the invention to provide a device for `converting electrical energy into mechanical motion wherein temperature changes in the surrounding atmosphere are ineffective to have any appreciable effect on the motion produced by the device.

A further object of the invention is to provide a device for converting electrical energy int-o mechanical movement, wherein the motion produced is closely regulated, without variation due to ambient temperature change or fluctuation in line vol-tage. In connection with the problem of motion regulation it is realized that certain of the previously developed devices control the motion by a spreading apart of the conductive particles during the expansion of the expansible material. Thus, the current flow through the dispersed electrically-conductive particles causes the expansion material to expand and thereby increase the spacing between adjacent conductive particles so as to etec'tively increase the electrical resistance to cur. rent ow and thereby choke ofi the current through the device. The action is such that after the cartridge has expanded la predetermined amount little or no current will l be drawn through the cartridge, and the motion will be limited. The cooling action of the ambient atmosphere will contract lthe cartridge to its initial low temperature" position 4for repetition of .the cycle.

However,` incertain installa-tions, when an excessivevoltage is lapplied across the cartridge the resultant-ly large he-at input tothe expansible material results in an inordi- ICC nately large thermal expansion and a correspondingly ex cessive motion. It is an object of the present invention to eliminate this diticulty.

A further object of the invention is to provide a device for converting electrical energy to mechanical motion, 'wherein an internal switch structure is provided for automatically cutting ott the current ow through the device 'at a predetermined point in the cycle so as to positively limit the motion produced.

An additional object of the invention is to provide a device for converting electrical energy into mechanical movement wherein economically constructed means are provided for controlling the beginning point of the' power stroke and end point of the power stroke, irrespective of variation in ambient temperature or applied voltage.

Other objects of this invention will appear in the follow# reference being had ing description and appended claims, 'to the accompanying drawings form-ing a part of this specication wherein like reference characters designate corresponding parts in the several views.

In the drawing: l

The single gure is a sectional view embodiment of the invention.

Before explaining the present invention in detail, it is to be understood that the invention is not limi-ted in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood thlatthe phraseology or terminology ernployed herein is for the purpose of description and not of limitation.

Referring to the drawing, there is shown a brass casing 10 comprising a generally cup-shaped casing element 12` having a peripheral flange 14 at its mouth for receiving a cover plate 16, elements 12 and 16 being secured together by an annular clamping ring 18; Plate 16v is provided 'with an opening which receives the sleeve-like extension 20 of 4a plastic insulator disk 22, ythe arrangement being suchtha-t a meta-l electrode disk 24 seats on disk 22, with .the electrode extension 26 projecting through the sleeve 20 for connection with an electrical lead (not shown).

The internal surface of casing element 12 is provided with a lining 28 of electrioalinsullating material which may be formed 4of glass enamel coating, a mica cylinder, plastic cylinder, or the like. Positioned within liner 28 is a cartridge 30 of electrically-conductive thermally-ex- 1 conductive particles in suspended positions evenly dis'- persed throughout the body of the cartridge.

The dispersed electrically-conductive particles m-ay be vformed of different conductive substances such as carbon, silicon, silicon carbide, lead sulfide, iron sulfide or metals such as copper and aluminum. The siz'e of the particles employed depends to a certain extent ori the material used. Metals are preferably used in particle sizes inthe range of 40 microns. Carbon black can be used inparticle sizes in the range of about 20-500 millimicrons. When the metals are employed they preferably comprise about of the cartridge volume. When carbon black is employed as the conductor it can be utilized in proportions of about 40% of the cartridge volume.

The thermally-expansible component of the cartridge mixture is a non-conductor and is preferably a solid material expansible in the operating range of the device toward a liquid condition. Among the materials which nent are branched and straight chain waxes, polyethylene,

Patented Apr.v 28, 1964 taken through one t ticles).

Various anti-oxidant materials and binder materials may be intermixed with the thermally-expansible component in minor Aproportions to prevent decomposition,

settling out of the conductive particles and otherwise insure proper operation. A particularly valuable antioxidant for use with polyethylene is p-(benzyloxy) phenol in about 0.5% concentration. Suitable binder materials are vinyl chloride polymer and diphenyl. It will be understood that the binder materials serve to increase the viscosity of the expansion material in its transition temperature range (particularly when the expansion material forms a relatively thin liquid), and to hold the dispersed conductive particles in an even dispersion throughout the body of the cartridge without settling out in a manner to provide uneven heating or short circuit around portions of the cartridge.

Movably disposed within liner 28 and adjacent one end of cartridge 30 is an electrode disk 32 of steel, brass, or other electrically conductive material. The central portion of the disk 32 is engaged with a piston-like electrode 34 slidably extending within a sleeve36, which is slidably extended through an opening 38 in the end wall of casing 12. The casing defines a tapering recess 40, in which is received an annular plug of force-transmitting material 42, said material preferably beingrubber or similar deformable substance which can change its shape in accordance with the movements of sleeve 36 and piston 34. Interposed between plug 42 and electrode disk 32 is an annular fiber spacer 44 having a rather tight sliding engagement with the liner 28 to prevent any extrusion of the rubber into the spacer-liner joint and to seal the expansion material within the cartridge 30.

Piston 34 is provided with an enlargement 46 which forms a seat for one end of a compression spring 48, the other end of spring 48 engaging a wall 50 of the device to be operated by the electrically-energized power unit.

Piston 34 may be utilized as an electrode for suitable connection with an electrical lead (not shown), or the brass casing 12 may be provided with a screw type terminal 51 to form a connection for the lead. In the illustrated arrangement current ow takes place from the electrode disk 24 through the dispersed electrically-conductive-resistive particles in cartridge 30, electrode disk 32, piston 34, electrically-conductive sleeve 36, casing 12, and screw terminal 51.

In operation of the power element, when the terminals 26 and 51 are connected into an electrical circuit the dispersed conductive particles within the cartridge 30 serve to form a large number -of conductive paths between the two electrode disks 24 and 32 so as to heat the thermally-expansible material in the cartridge and move the disk 32 and spacer 44 outwardly of the casing 12. The initial outward movement of disk 32 and spacer 44 puts an increased pressure on the annular deformable plug 42, and this pressure is transmitted to the sleeve 36, the arrangement being such that the sleeve is forced upwardly relative to the piston 34. It will be noted that sleeve 36 is oatingly suspended within the plug 42, whereas the piston 34 has the force of spring 48 behind it to urge it into pressure engagement with the electrode disk 32. Thus, the sleeve 36 is forced outwardly on the piston 34 until it strikes enlargement 46. It will be understood that during this period there is a slight movement of the piston 34 under the force of disk 32. However, since the area of disk 32 is many times the area of sleeve 36 the volumetric displacement of plug 42 is such that sleeve 36 engages the enlarge- 4 ment 46 prior to any substantial movement of the piston 34.

The above described arrangement of parts is particularly advantageous in providing a lost motion connection during the initial expansion of the expansible material in cartridge 30; thus, if the ambient temperature should increase so as to have a substantial eiect on the cartridge 30 then this effect will be taken up by the lost motion travel of sleeve 36 toward enlargement 46 in a manner to preclude the piston 34 from moving substantially in response to ambient temperature increase. In this manner the power element is made responsive to electrical energy input without deviation in performance due to changes in ambient temperature.

During the input of electrical energy into cartridge 30, after sleeve 36 engages enlargement 46 thesleeve is prevented from movement relative to piston 34, and the movement of disk 32 is therefore transmitted entirely to the piston-sleeve assembly via the plug 42. Due to the difference in area of disk 32 and sleeve 36 the sleevepiston assembly has a magnified movement relative to the movement of the disk 32. It should be understood that the sleeve-piston assembly is moved by the squeezing action of plug 42 on the lower face 43 of the sleeve, and that the sleeve-piston assembly has movement relative to the disk 32. As the piston 34 leaves contact with disk 32 the electrical current flow through the device is discontinued. `However, the heat developed by the earlier ow of current through the conductive resistive particles continues to be effective to expand cartridge 30 and move the piston-sleeve assembly to the location wherein enlargement 46 takes approximately the position 46a.

It will be seen that with the above described construction the flow of electrical current through the device is very accurately regulated in accordance with the position of disk 32, i.e. when the disk 32 reaches a predetermined position the sleeve-piston assembly is automatically moved out of engagement with the disk to discontinue current flow. By this arrangement possibility of an undesired current ow through a small portion of the cartridge 30 is eliminated. Such undesired current ow (without the internal switch arrangement provided by disk 32 and piston 34) would pose the possibility of a. run-away condition of the piston (i.e. an excessive outward movement of the piston tending to break the parts and/or destroy the calibration of the device).

The disclosed internal switch arrangement is particularly advantageous in guarding against the effects of wide fluctuations in line voltage conditions. Thus, any sudden drastic increase in line voltage is effective to move the disk 32 outwardly for squeezing the material 42 and breaking the circuit between elements 32 and 34.

During the cooling cycle of the power element the spring 48 returns piston 34 into `contact with the electrode disk 32 so as to re-establish the electric circuit and thereby provide a repeat of the power stroke. During the cooling cycle the sleeve 36 may or may not leave the enlargement 46 and return to its illustrated position. Whether or not the sleeve leaves enlargement 46 is mmaterial to operation of the device since the low temperature position of the piston 34 is controlled only by the spring 48 and the contracted volume of the cartridge 30.

From the above description it will be seen that sleeve` 36 functions as a lost motion connection between the cartridge 30 and the piston 34 during the initial stages of cartridge expansion. Thus, the sleeve 36 serves as a control device for cancelling out the effect of variations in the ambient temperature on the piston motion achieved during ythe electrical heating operation.

Piston 34 cooperates with the disk 32 to provide an electric switch structure internally of the power element, the purpose of this switch structure being to limi-t the amount of cartridge heating and the effect of excessive voltages thereon.

' illustrated construction may -be resorted to vwithout despirit of the invention 'as delined in the parting from the appended claims.

I claim:

l. In a power device, l

.an electrically lconductive casing carrying a rst electrode on one end in electrically isolated relation,

an electrically conductive, thermally expandable power element within said casing in electrical connection 'with lsaid first elect-rode,

an electrically conductive plate movable in said casing against one end of said element to receive the force thereof,

,an electrically conductive piston movably mounted in the other end of said casing and having one end engageable with said plate Iand the other end projecting beyond said casing,

' said piston `being in electrical contact with said casing,

a sleeve -slidably mounted on said piston,

a body of force transmitting material surrounding said sleeve in the space ybetween the said plate and the other end of said casing,

,lost motion means between said sleeve and said piston accommodating initial 4force transmitted by said force transmitting material, v

and fan electrode on said casing forming a circuit .through said device'.

2. A thermal expansion device comprising a casing having a movable piston projecting therebeyond, thermal expansion material within said casing, force-transmitting material disposed within said casing, a oating member in extended surface contact with the forcedransrnitting material for movement thereby at operating temperatures of the expansion material, said 'ating member being interposedbetween the force-transmitting material and the piston, and lost motion means accommodating relative piston-member movement at low operating temperatures of the expansion material and joint piston-member movement at higher operating temperatures of the expansion material.

3. A thermal expansion device comprising a casing, a`

movable piston having one end projecting into said casing and another end projecting -therebeyond, thermal expansion material within said casing, an elastomeric forcetransmitting plug disposed within said casing and surrounding the one end of said rod, an annular sleeve interposed between the force-transmitting material and the piston, and means accommodating relative piston-sleeve movement :at low operating temperatures of the expansion material land joint piston-sleeve movement at higher operating temperatures of the expansion material.

4. A thermal responsive device comprising a casing, a thermally expansible power element disposed within said casing, 'a force-transmitting piston having one end projecting beyond said casing and the other end projecting into said casing, an elastomeric plug surrounding said other end of said piston and subjected to thermal expansion of said power element, and la lost motion connection between said power element and said piston to accommodate initial power element expansion without piston displacement, said connection including a sleeve interposed between said plug and said other end of said piston and freely movable relative to the piston fupon initial expansion of said power element.

5. A thermal responsive device comprising a casing, a thermally expansible power element disposed within said casing, a forcetnansmitting piston having one end projecting beyond said casing and the other end projecting into said casing, lan elastomeric plug surrounding said other end of said piston and subjected to thermal expansion of said power element, and a lost motion connection between said power element and said pistonto accommodate initial power element expansion without piston dis-- placement, said connection including an abutment "on said piston one end exteriorly' of said casing anda sleeve inf terposed between said plug and said other end of said piston and freely movable relative to the piston until coming into contact with said abutment upon initial expansion of said power element, said sleeve and said piston being thereafter jointly movable.

6. A device for converting electrical energy into mechanical movement, comprising a casing; an electrically conductive, thermally expansible power element disposed within said c-asing; a piston having one end disposed within said casing and :another end projecting therebeyond;

means lfor passing an electrical current through said power element to thermally expand the same, said means including an electrode plate contacting said power element and said piston to complete the circuit for expanding said power element; an elastomeric plug disposed within said casing for'compression upon expansion of said element; a forcetransmitting element interposed between said plug and said piston and having one end disposed within said easing tol be substantially surrounded by said plug and having another end projecting beyond the casing, expansion of said element and compressionof said plug displacing said force-transmitting element outwardly of said casing; and lost-motion means interconnecting said force-transmitting element and said piston for joint movement after initial displacement of said force-transmitting element,

such joint movement breaking the plate-to-piston contact,

thereby interrupting current flow through said ment.

7. In a thermal responsive device,

a casing,

power elean electrically conductive, thermally expandable power chanical movement, comprising a casing; an electrically'` conductive, thermally' expansible power element disposed within said casing; means for passing an electrical current through said power element to thermally expand the same; an elastomeric plug disposed within said casing 'for compression upon expansion of said element; and a force-transmitting element having one end disposed within said casing to be substantially surrounded by said plug and having another end projecting beyond the casing, expansion of said element and compression of said plugdisplacing said force-transmitting element outwardly of said casing.

9. The combination comprising fa casing structure having an electrically-energized thermally-expansible cartridge therein comprised of dispersed conductive particles within a non-conductive expansion material; a switch structure within said casing including a conductive disk engaged with the expansible cartridge and a conductive plunger of lesser diameter than the disk; a sleeve oatingly surrounding said plunger; cooperating means on the sleeve and plunger for limiting relative movement between the sleeve and plungenand a body of elastomeric forcetransmitting material within the casing surrounding the sleeve whereby, on expansion of the cartridge the forcetransmitting material initially forces the sleeve outwardly on the plunger, and thereafter forces the sleeve-piston assembly away from the disk.

10. In a thermal responsive device,

a casing,

' a thermally expandable power element disposed within said casing,

a movable piston having one end projecting into said casing and into positive contact with said power ele- Intent,

and lost motion connection means between said pdston and said power element accommodating initial power element expansion without rela-tive pistonpower element displacement and subsequent power element expansion with relative piston-power element displacement.

References Cited in the file of this patent UNITED STATES PATENTS 2,781,784 Baker Feb. 19,v 1957 2,835,634 Vernet et al May 20, 1958 2,883,490 Larson Apr. 21, 1959 3,016,691 Asakawa et al. Jan. 16, 1962 

11. IN A THERMAL RESPONSE DEVICE, A CASING, A THERMALLY EXPANDABLE POWER ELEMENT DISPOSED WITHIN SAID CASING, A MOVABLE PISTON HAVING ONE END PROJECTING INTO SAID CASING AND INTO POSITIVE CONTACT WITH SAID POWER ELEMENT, AND LOST MOTION CONNECTION MEANS BETWEEN SAID PISTON AND SAID POWER ELEMENT ACCOMMODATING INITIAL POWER ELEMENT EXPANSION WITHOUT RELATIVE PISTONPOWER ELEMENT DISPLACEMENT AND SUBSEQUENT POWER ELEMENT EXPANSION WITH RELATIVE PISTON-POWER ELEMENT DISPLACEMENT. 